Electron discharge device cathode assembly



c. v. LITTN ELECTRON DISCHARGE DEVICE CATHODEVASSEMBLY Filed May 8, 1950 INVENTOR ATTORNEY .lllllllll CHARLES M LITTON May 4, l1954 CNTROL wwr Patented May 4, r1954 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE CATHODE ASSEMBLY Charles V. Litton, Redwood City, Calif. Application May 8, 1950, Serial No. 160,750

4 Claims. 1

This invention relates to electron discharge device electrodes and more particularly to cathode assemblies for electron discharge devices.

In certain types of electron discharge devices cathodes thereof are sometimes subject to overheating. I'his is particularly true in the case of magnetrons operated at a low duty cycle, in which the cathode tends to become overheated by electron bombardment at times when the anode potential is low.

In magnetrons this overheating effect has been noted. One system proposed for overcoming it provides a light permeable window, which can pick up light from the cathode filament and control the filament supply in accordance therewith. However, in tunable magnetrons inserts are often moved within the resonator areas, these inserts or plungers acting like light shutters so that optical devices are not satisfactory.

In some cases it has been noted that a cathode may be maintained at emissive temperature by bombardment, and it has been the practice to disconnect the heater leads upon this temperature being reached. One system has been proposed, having a cathode external of the anode and provided with a thermostatic switch to open the cathode heater leads under control of cathode heating. This system does not adjustably control the heating current supplied to the cathode, however, to maintain a substantially uniform operation.

It is an object of my invention to provide a cathode assembly for an electron discharge device which incorporates therein a heat responsive coupling element for adjustably controlling the heater current supply.

In accordance with my invention I provide a heat sensitive device in the cathode assembly of an electron discharge device adjacent the emitting surface which device may be used adjustably to regulate the external heater current supply of the cathode.

In cathode assemblies of the type in which a centrally mounted substantially cylindrical emitter is used the heat sensitive device is mounted within the cylinder, preferably at a point adjacent the surface subject to heating by back bombardment. The heat sensitive device may constitute a connection between the conductor supporting the emissive material and another conductor which exhibits substantial thermoelectric properties upon connection to the metal of the conductor.

In another form a thermocouple may be made between the heating filament support rod and a second conductor at a point within the cylindrical cathode. The leads for the thermocouple may constitute the support rod, and a cylindrical sleeve mounted about said rod, or a wire connected to the rod.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a fragmentary sectional view of a portion of a magnetron, together with a diagrammatic showing of circuit connections illustrating the principles of my invention; and

Figs. 2 and 3 are fragmentary views of a portion of the cathode assembly illustrating modified forms of the invention illustrated in Fig. l.

Turning to Fig. 1 a portion of a magnetron casing I, and a resonator vane 2 are shown associated with a cathode assembly 3. Cathode assembly 3 may comprise a cylinder for carrying an electron emissive coating 5 which may be heated by a iilamentary heater 6 supported by a support rod l. Support rod l may be directly connected to cathode hat portion 8 which in turn is electrically connected with the cylinder 4. The lower portion of the cathode assembly 3 is substantially enclosed by a second shielding hat 9 through which are sealed support conductor 'I and filament feed line I l). The central support rod 'l and filament leads Il) may be connected to a portion II of a supply potentiometer I2 for adjustment to the heating current flowing through the heater nlament E. The other end of potentiometer I2 may be coupled through more variable supply means I3 to magnetron anode wire 2. The variable supply means may for example, be a pulse source which serves to Vary the energization of the magnetron and may supply voltage in the form of pulses for intermittent operation of the magnetron. Under these conditions of operation the normal magnetic field of the magnetron may serve to drive the free electrons to the cathode with considerable force at the periods when the anode is not energized causing excessive heating. This heating will vary dependent upon the elciency of operation of the magnetron and the total duty cycle of the equipment dependent upon the pulse rate. In order that this excess heating may be avoided I provide a second conductor I i extending within cathode assembly 3 and welded at point I5 with rod l. Conductor It and rod 'I which are of different metals which would connect together will produce a substantial terminal electric current. For example, the support rod may be of tungsten and the sleeve of molybdenum. Preferably the weld i5 is arranged at the maximum heating point within the housing defined by cathode assembly 3 and will be somewhere near the center of the emissive area 5 of the cathode. The thermally produced currents may be applied over leads It to a control unit il which serves through a mechanical coupling indicated by dotted line 28 to adjust a potentiometer slider 20 along portion Il of potentiometer I2 so as to control the amount of current supplied to the heater filament S under control of the current obtained by the thermocouple. The control unit l may comprise any known type of servo mechanism and details are not illustrated here as it is considered this is too well known to need complete illustration.

While the structural arrangement of Fig. l is simple to make it is clear that there will be considerable heat dissipation from a sleeve l@ and therefore the device may be somewhat sluggish when responding to overheating effects on the cathode assembly. In order to improve the rapidity with which the device will respond the thermosensitive element may comprise a thermocouple of the type shown in Fig. 2. In this arrangement a wire 2i of the same material as support rod l, for example, tungsten, may be welded to the rod and a wire 22 of different material such as molybdenum, may be coupled thereto at 23 to provide a thermocouple. Since the wire 22 may be relatively fine this device will be much more sensitive to temperature changes and will respond with greater rapidity. If desired wire 22 could be directly welded to rod l as in the case of the sleeve Iii of Fig. l. However, the extension wire may be desired so that the thermocouple is coupled closer to the emissive surface E.

In Figs. l and 2 the thermocouple has been illustrated as being made between support rod 'i' and some other metal. However, a further modification is shown in Fig. 3 wherein the thermocouple is effective between the cylindrical member 4 and a support conductor 24.. The conductor 24 may if desired be in the form of a ring welded to cylinder 4 internally thereof. A lead wire 25 may be connected to this ring 2li at one or more points. Since there is electrical connection to cylinder 4 through hat 8 and rod 1, rod 'E may in this instance also serve as one of the output leads for the thermally derived currents. It will be understood that the support rod may serve the triple function of return lead for the lament heater, cathode supply for the tube itself and a return lead for the thermocurrents.

While I have disclosed in the various embodiments illustrated a thermo-sensitive element in the form of a thermocouple, it is clear that other ty es of thermal sensitive elements may be used if desired. Likewise the invention may be applied to other types of cathode construction al.- though it is particularly useful in the cylindrical type of indirectly heated cathode as illustrated. The principles of my invention apply not only to magnetron constructions but to any type of cathode assembly wherein the problem of regulation to avoid overheating is present.

What is claimed is:

l. A cathode assembly comprising hollow.1 metallic sleeve supporting member, an electron emitting coating on the outer surface of said sleeve, a metallic rod supporting member connected tc said sleeve, a cathode heater lead connectcd at one end to said rod whereby said rod serves as a cathode heater return lead, and a metal element exhibiting thcrmoelectric properties with respect to the metal of said supportinflr members conductively joined with one of s members within said sleeve and intermediate le ends thereof, whereby a thermocouple for controlling heating of said cathode is provided.

2. A cathode assembly according to claim l, wherein said metal element is joined with the inner surface of said hollow metallic sleeve.

3. A cathode assembly according to claim l, wherein said metal element is joined with said rod.

li. A cathode assembly according to claim 3, wherein said metal element comprises a sleeve o1" said second metal surrounding said support rod.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,787,300 Alexanderson Dec. 30, 1930 2,130,380 Clark Sept. 20, 1938 2,372,037 Watrous Mar. 20, 194.5 2,437,880 Kusch Mar. i6, 1948 2,481,061 Anderson Sept. 6, 1949 2,522,259 Fay Sept. 12, 1950 

